O2 to be a friend or foe?

Hyperoxia

Clinicians should titrate O2 therapy to avoid both hypoxemia and hyperoxia. While the harmful effects of tissue hypoxia are clearly understood, over-correction leads to tissue hyperoxia, which may also be hazardous. Hyperoxia injuries cause oxidant stress with pro-inflammatory and cytotoxic effects. It appears prudent to target PaO2 values within an acceptable range, particularly as no clinically useful biomarker of O2 toxicity is available, and data on the effects of hyperoxia on markers of oxidative stress are equivocal.

While “optimal” dosing of oxygen remains unclear, it is known that you can have too much of a good thing.  The Oxygen-ICU trial was the first major study to suggest clinically important harm from liberal O2 administration in a general ICU population. This single-center, RCT included 480 patients expected to stay in the ICU for at least 72 hrs. The ICU mortality was 20.2% with conventional and 11.6% with conservative O2 therapy. Conversely, the LUNGSAFE study found no relationship between hyperoxia or excessive oxygen use and patient outcome. These conflicting results show the lack of informational studies on high concentrations of FiO2 use and hyperoxia. While severe degrees of systemic hypoxia associated with harm in other critically ill populations are not possible in ARDS, it is unclear that high concentrations of FiO2 exacerbate the disease process. 

Oxygen is not a harmless drug and its use should be treated as though it can have adverse side effects. Conservative oxygenation strategy target SpO2 of 90–92% should be utilized, as it was associated with lower incidence of new organ dysfunction. It seems clear that FiO2 should not be fixed, but rather titrated to achieve PaO2 or SpO2 targets. There is no reason to keep FiO2 high when SpO2 is 100% or at a satisfactory level for the patient.  Weaning oxygen should be immediately considered once a reasonable PaO2 level is achieved. Targeted PaO2 by disease process has not been largely studied, but the need is there. Respiratory Therapists should always be aware of the perils of hyperoxia and adjust therapy accordingly.